[Clas12_software] [Clas_offline] Meeting today

[Mac Mestayer]

Hello Dennis;

Yelena and I will be meeting next Monday to discuss geometry
issues.  I append a previous email in the hopes it might be
helpful to other geometry service projects.  I may not be
able to make the meeting because of a conflict with
Dave's CLAS12 TDG meeting.

 			- Mac

"mestayer at jlab.org", (757)-269-7252

>From mestayer at jlab.org Wed Sep  2 09:56:09 2009
Date: Wed, 2 Sep 2009 09:56:08 -0400 (EDT)
From: Mac Mestayer <mestayer at jlab.org>
To: Yelena Prok <yprok at jlab.org>
Cc: Dave Heddle <heddle at jlab.org>, Vardan Gyurjyan <gurjyan at jlab.org>, Dennis Weygand <weygand at jlab.org>, Sebastien Procureur <procureu at jlab.org>, Maurizio Ungaro <ungaro at jlab.org>, clas_offline at jlab.org, clas12_software at jlab.org
Subject: CLAS12 geometry service

Hello Yelena;

I've been thinking about the data structures and methods
of tracking in general, and also specifically with regards
to geometry information.

First, I think it would be useful if we formally name and
describe a new coordinate system in which the new z-axis
lies in the sector mid-plane and is perpendicular to the
drift chamber wire planes (i.e. along a 25 deg. polar angle).
The new x-axis would also lie in the sector mid-plane.
We might call this the sector wire plane coordinate system.
In this coordinate system, the wire planes are defined by
a z-value only.

Here are a number of services I think the package should provide:
- given a point in the sector coordinate system, return a point
in the sector wire plane coordinate system
- return the nearest wire plane in the +z direction, as well as
the distance to that plane
- if the user also specifies a direction cosine in additon to the
space point, we could return the distance to the nearest plane along
that direction vector, as well as the point of intersection of the
line and plane
- we could also return the distance to the nearest two wires for the
point in the plane; perhaps both the distance as well as the distance
along x.

One of our customers would likely be a track-fitter, which might
like to swim a track to the nearest plane and determine the intersection
point on that plane, and then determine the nearest two wires (in the
plus and minus x-direction), and then determine the distance of closest
approach to the wires in question.  This operation would be repeated many
times, so it needs to be fast.

Another customer might be the graphics package from the event display
program, and that customer might have more requests.

Of course, we already have a gemc customer, that needs locations and
definition of wire plane pseudo-volumes.

Anyway, I wanted to start the dialog.  The associated objects might
be Wire and WirePlane, etc. for example.  First, I wanted to find out
what track fitters and track simulators need from the geometry service,
so I cc'd Sebastien and Dave and Maurizio and others.

Comments, anyone?			- Mac

"mestayer at jlab.org", (757)-269-7252

On Tue, 6 Oct 2009, Dennis Weygand wrote:

> Our meeting time today is 11:00 EST.
> No one suggested any agenda items, therefore:
> There is a CLAS12 Steering Committee meeting tomorrow, so let's
> discuss status of various projects.
>
> Also, as always, and status of the svn conversion.
>
> Dennis
>
> --
> Dennis Weygand
> weygand at jlab.org
> (757) 269-5926
>
>
>
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